1) Absolutely go see it. You never know. I once rushed down to my boutique to see a bunch of Kellys convinced of which I would take (Raisin GHW). I left with a totally different bag that made my heart sing and that I still love (Gold PHW). Also IMO Bleu Électrique looks best with PHW.
2) That said.....read up on Tadelakt. It is a bit like Box, it is delicate, it will scratch. To me this is the bigger issue. Tadelakt is totally different to other leathers you were considering. The bag will be BEAUTIFUL (I would have a hard time saying no) but not a workhorse.
3) Agreed, BE is out there. It is always on the SO list and I haven't seen a season without it in my H history. A bag may well show up in GHW and your favorite leather. For me though if I can't get a color I love in the right specs I satisfy myself with another piece (for instance, I couldn't find BE in a Kelly as I wanted, and was a little scared of the "pop" color, so I bought it in an Evie TPM which I wear constantly). So, perhaps, you find a dream Birkin, but not BE....you can always find something in BE.